Substrate Integrated Waveguide Filtering Rat-Race Coupler Using Dual-Mode Composite Cavity

This letter presents a compact substrate integrated waveguide (SIW) filtering rat-race coupler based on a dual-mode composite cavity (DMCC) and stacked SIW cavities (SIWCs). The dual-mode characteristics of the DMCC are systematically analyzed to guide the circuit realization. By incorporating two coupling windows between the DMCC and stacked SIWCs, the internal couplings for the TE₁₀₁ and folded TE₁₀₁ (FTE₁₀₁) modes can be independently controlled, significantly reducing the design complexity of the SIW filtering rat-race coupler. To validate the design, a second-order SIW filtering rat-race coupler is designed, fabricated, and measured. The measured results agree well with the simulated ones.